JP2009235950A - Control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely inhibit emission of HC to atmospheric air even if misfire occurs when exhaust emission control catalyst is not activated yet in a control device for an internal combustion engine. <P>SOLUTION: This control device for the internal combustion engine is provided with an EGR passage connecting an exhaust gas passage and an intake air passage, an EGR valve opening and closing the EGR passage, a crank angle sensor detecting rotation angle of a crankshaft of the internal combustion engine, a misfire detection means detecting the occurrence of misfire based on signal of the crank angle sensor, and an unburned gas recirculation means temporally opening the EGR valve so at to make unburned gas discharged from a cylinder in which the misfire occurs recirculate to the intake air passage through the EGR passage if misfire is detected by the misfire detection means when EGR is stopped by closing the EGR valve. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a control device for an internal combustion engine.

  In Japanese Patent Laid-Open No. 2001-241353, an instantaneous minimum rotational speed and an instantaneous maximum rotational speed during an expansion stroke for each cylinder are calculated based on a signal from a crank angle sensor, and a rotational fluctuation deviation for each cylinder is calculated based on these. An apparatus for detecting a misfired cylinder by calculating the above is disclosed.

JP 2001-241353 A Japanese Patent Laid-Open No. 11-241630 JP 2004-225654 A JP-A-11-159362 JP 2000-120478 A JP 2004-92603 A

  As is well known, immediately after the cold start, since the exhaust purification catalyst is low temperature and not activated, harmful components in the exhaust gas cannot be sufficiently purified. For this reason, conventionally, reduction of emissions when the exhaust purification catalyst is inactive has become a very important issue.

  When misfire occurs, unburned gas is discharged as exhaust gas from the misfired cylinder. Unburned gas contains a large amount of HC. Therefore, there is a problem that a large amount of HC is released into the atmosphere without being purified when an accidental misfire occurs immediately after a cold start when the exhaust purification catalyst is not activated. The above-mentioned conventional publication does not disclose any countermeasures against such problems.

  The present invention has been made to solve the above-described problems, and reliably suppresses the release of HC into the atmosphere even when a misfire occurs when the exhaust purification catalyst is inactive. An object of the present invention is to provide a control device for an internal combustion engine.

In order to achieve the above object, a first invention is a control device for an internal combustion engine,
An EGR passage connecting an exhaust passage and an intake passage of the internal combustion engine;
An EGR valve that opens and closes the EGR passage;
A crank angle sensor for detecting a rotation angle of a crankshaft of the internal combustion engine;
Misfire detection means for detecting the occurrence of misfire based on the signal of the crank angle sensor;
When the EGR is stopped by closing the EGR valve, if misfire is detected by the misfire detection means, unburned gas discharged from the misfired cylinder passes through the EGR passage and the intake passage. Unburned gas recirculation means for temporarily opening the EGR valve so as to recirculate to
It is characterized by providing.

The second invention is the first invention, wherein
A transport delay time calculating means for calculating a transport delay time of the exhaust gas from the exhaust valve to the EGR passage;
The unburned gas recirculation means opens the EGR valve during a period in which an exhaust valve opening period of the misfired cylinder is delayed by the calculated transport delay time.

The third invention is the second invention, wherein
Air-fuel ratio detecting means for detecting the air-fuel ratio;
Learning means for acquiring a learning value for correcting the transport delay time based on a detection result of the air-fuel ratio detection means;
Transport delay time correcting means for correcting the transport delay time based on the learned value;
It is characterized by providing.

According to a fourth invention, in any one of the first to third inventions,
In the internal combustion engine, exhaust valve opening periods of a plurality of cylinders overlap in time,
When the EGR valve is temporarily opened by the unburned gas recirculation means, the exhaust valve opening overlapping the exhaust valve opening period of the misfired cylinder is added to the gas recirculating to the intake passage through the EGR passage. An inert gas ratio calculating means for calculating a ratio of the inert gas discharged from the cylinder having the valve period;
Fuel injection amount correcting means for correcting the fuel injection amount based on the ratio calculated by the inert gas ratio calculating means;
It is characterized by providing.

The fifth invention is a control device for an internal combustion engine,
A bypass passage for bypassing the exhaust passage of the internal combustion engine;
An HC adsorbent provided in the bypass passage and having a function of adsorbing HC in the exhaust gas;
A flow path switching valve that switches between a state of flowing exhaust gas through the bypass passage and a state of not flowing the exhaust gas;
A crank angle sensor for detecting a rotation angle of a crankshaft of the internal combustion engine;
Misfire detection means for detecting the occurrence of misfire based on the signal of the crank angle sensor;
When the misfire is detected by the misfire detection means without always flowing the exhaust gas through the bypass passage, the unburned gas discharged from the misfired cylinder is caused to flow temporarily through the bypass passage. Adsorbing control means for controlling the flow path switching valve so as to pass through the HC adsorbent,
It is characterized by providing.

According to a sixth invention, in any one of the first to fifth inventions,
The misfire detection means detects the occurrence of misfire based on an average crank angular acceleration in a crank angle section in which an average value of inertia torque due to reciprocating inertial mass of the internal combustion engine is substantially zero.

  According to the first invention, for example, when a misfire is detected in a state where the external EGR is stopped just after a cold start, unburned gas discharged from the misfired cylinder passes through the EGR passage. Thus, the EGR valve can be temporarily opened so as to return to the intake passage. As a result, the unburned gas discharged from the misfired cylinder can be recirculated to the combustion chamber and burned, so even if the exhaust purification catalyst is inactive, HC in the unburned gas is released into the atmosphere. This can be reliably suppressed. In the above case, the main reason for recirculation to the combustion chamber is not an inert gas but an unburned gas (that is, a mixture of fuel and air). For this reason, even if the EGR valve is temporarily opened, the change in the air-fuel ratio in the combustion chamber is suppressed, so that combustion does not become unstable. Therefore, it is possible to reliably suppress the occurrence of operation failure.

  According to the second invention, it is possible to calculate the transport delay time of the exhaust gas from the exhaust valve to the EGR passage, and to control the EGR valve based on the transport delay time. Thereby, the unburned gas discharged | emitted from the misfire cylinder can be correctly flowed into an EGR channel | path.

  According to the third aspect, it is possible to acquire a learning value for correcting the transportation delay time based on the detection result of the air-fuel ratio detection means, and to correct the transportation delay time based on the learned value. Thereby, the calculation error of the transportation delay time caused by the secular change can be accurately corrected. Therefore, the unburned gas discharged from the misfire cylinder can be more accurately flowed into the EGR passage.

  According to the fourth invention, even in the case of a multi-cylinder internal combustion engine in which the exhaust valve opening periods of a plurality of cylinders overlap in time, when the unburned gas discharged from the misfire cylinder is recirculated to the intake passage, Variations in the air-fuel ratio in the combustion chamber can be reliably suppressed.

  According to the fifth invention, for example, when a misfire is detected in a state in which the external EGR is stopped, for example, immediately after a cold start, the unburned gas discharged from the misfired cylinder enters the bypass passage. The flow path switching valve can be controlled so as to pass through the arranged HC adsorbent. As a result, HC in the unburned gas discharged from the misfired cylinder can be adsorbed by the HC adsorbent, so even if the exhaust purification catalyst is inactive, the HC in the unburned gas is released into the atmosphere. Can be reliably suppressed. In addition, since the time for exhaust gas to flow through the HC adsorbent can be minimized, the HC adsorbent is filled with HC, or the temperature of the HC adsorbent rises and the adsorbed HC is released. This can be surely prevented.

  According to the sixth aspect of the invention, it is possible to detect the occurrence of misfire based on the average crank angular acceleration in the crank angle section where the average value of the inertia torque due to the reciprocating inertia mass of the internal combustion engine is substantially zero. Thereby, the occurrence of misfire and the misfire cylinder can be detected with high accuracy without using a special sensor.

Embodiment 1 FIG.
[Description of system configuration]
FIG. 1 is a diagram for explaining the configuration of the system according to the first embodiment of the present invention. The system shown in FIG. 1 includes an internal combustion engine 10 mounted on a vehicle. The internal combustion engine 10 of the present embodiment is assumed to be an in-line four cylinder type. FIG. 1 shows a cross section of one of the cylinders. A piston 12 is provided in each cylinder of the internal combustion engine 10. An intake passage 16 and an exhaust passage 18 communicate with each cylinder.

  In the middle of the intake passage 16, an electronically controlled throttle valve 20 and a surge tank 22 are provided. The surge tank 22 is disposed on the downstream side of the throttle valve 20. An air flow meter 23 for detecting the intake air amount is installed on the upstream side of the throttle valve 20. An exhaust purification catalyst 26 for purifying exhaust gas is disposed in the exhaust passage 18.

  Each cylinder of the internal combustion engine 10 is provided with a fuel injector 28 for injecting fuel into the intake port, an ignition plug 30 for igniting the air-fuel mixture in the combustion chamber, an intake valve 32, and an exhaust valve 36. Yes. In the present invention, an in-cylinder injector that directly injects fuel into the cylinder may be provided instead of or together with the fuel injector 28.

  A crank angle sensor 42 for detecting the rotation angle (crank angle) of the crankshaft 24 is provided in the vicinity of the crankshaft 24 of the internal combustion engine 10. An accelerator position sensor 44 for detecting the accelerator pedal position is provided in the vicinity of the accelerator pedal.

  In addition, the internal combustion engine 10 includes an EGR passage 46 for performing so-called external EGR (Exhaust Gas Recirculation) for returning the exhaust gas in the exhaust passage 18 to the intake passage 16. One end of the EGR passage 46 is connected to the exhaust passage 18, and the other end of the EGR passage 46 is connected to the intake passage 16 on the downstream side of the surge tank 22. An EGR valve 48 for controlling the exhaust gas recirculation amount by opening and closing the EGR passage 46 is provided in the middle of the EGR passage 46.

  The system of this embodiment further includes an ECU (Electronic Control Unit) 50, a water temperature sensor 52 that detects the cooling water temperature of the internal combustion engine 10, and an air-fuel ratio sensor 54 that detects the air-fuel ratio of the exhaust gas. The ECU 50 is electrically connected to the various sensors and actuators described above.

  The ECU 50 has a function of calculating the angular acceleration of the crankshaft 24 based on the signal of the crank angle sensor 42 and detecting the occurrence of misfire based on the angular acceleration. Hereinafter, a method for calculating the angular acceleration of the crankshaft 24 in the present embodiment will be described.

The indicated torque T _i of the internal combustion engine 10 can be expressed by the following equations (1) and (2).

(2) the right side of the equation represents a torque that generates the indicated torque T _i, (1) the right side of the equation indicates the torque consuming indicated torque T _i.

(1) On the right side of the formula, J is the moment of inertia of the driven member driven by the combustion or the like of the mixture, d [omega / dt is the angular acceleration of the crankshaft 24, T _f is the friction torque of the drive unit, T _l is the time of running The load torque received from the road surface is shown. Here, J × (dω / dt) is a dynamic loss torque caused by the angular acceleration of the crankshaft 24. The friction torque _Tf is a torque due to mechanical friction of each fitting portion such as friction between the piston 12 and the inner wall of the cylinder, and includes torque due to mechanical friction of auxiliary machinery. The load torque _Tl is a torque due to a disturbance such as a road surface condition during traveling. In this embodiment, in order to detect misfire in the idle state after the cold start, T _l = 0 in the following description.

In the right side of the equation (2), T _gas indicates torque due to cylinder cylinder gas pressure, and T _inertia indicates inertia torque due to reciprocating inertial mass such as the piston 12. Torque T _gas due to in-cylinder gas pressure is torque generated by combustion of the air-fuel mixture in the cylinder.

As shown in the equation (1), the indicated torque T _i is obtained as the sum of dynamic loss torque J × (dω / dt) due to angular acceleration, friction torque T _f , and load torque T _l. it can.

FIG. 2 is a characteristic diagram showing the relationship between each torque and crank angle in equation (2). In FIG. 2, the vertical axis of the torque magnitude, the horizontal axis represents the crank angle, the one-dot chain line indicated torque T _i in FIG. 2, solid lines a torque T _gas by the in-cylinder gas pressure, the broken lines Indicates the inertia torque T _inertia due to the reciprocating inertia mass. Here, FIG. 2 shows the characteristics in the case of a four-cylinder engine. TDC and BDC in FIG. 2 are the top dead center (TDC) or the bottom dead center of the piston 12 of one of the four cylinders. The crank angle (0 °, 180 °) in the case of the point (BDC) is shown. When the internal combustion engine 10 has four cylinders, an expansion stroke is performed for each cylinder every time the crankshaft 24 rotates 180 °, and torque characteristics from TDC to BDC in FIG. 2 repeatedly appear for each expansion stroke.

As shown by the solid line in FIG. 2, the torque T _gas due to the in-cylinder gas pressure rapidly increases and decreases between TDC and BDC. Here, the rapid increase in T _gas is because the air-fuel mixture in the combustion chamber explodes (combusts). After the explosion, T _gas decreases and takes a negative value due to the influence of the cylinders in other compression strokes or exhaust strokes. When the crank angle reaches BDC, the change in the volume of the cylinder becomes zero, whereby T _gas takes a value of zero.

On the other hand, the inertia torque T _inertia due to the reciprocating inertia mass is an inertia torque generated by the inertia mass of the reciprocating member such as the piston 12 irrespective of the torque T _gas due to the in-cylinder gas pressure. The reciprocating member repeats acceleration / deceleration, and T _inertia always occurs as long as the crankshaft 24 rotates, even when the angular velocity is constant. As shown by the broken line in FIG. 2, the member that reciprocates is stopped at the position where the crank angle is TDC, and T _inertia = 0. When the crank angle advances from TDC toward BDC, the reciprocating member starts to move from the stopped state. At this time, T _inertia increases in the negative direction due to the _inertia of these members. When the crank angle reaches around 90 °, the reciprocating members are moving at a predetermined speed, so that the crankshaft 24 is rotated by the inertia of these members. Therefore, T _inertia changes from a negative value to a positive value between TDC and BDC. After that, when the crank angle reaches BDC, the reciprocating member stops and T _inertia = 0.

As shown in the equation (2), the indicated torque T _i is the sum of the torque T _gas due to the in-cylinder gas pressure and the inertia torque T _inertia due to the reciprocating inertia mass. For this reason, as shown by the one-dot chain line in FIG. 2, between TDC and BDC, the indicated torque T _i increases as T _gas increases due to the explosion of the mixture, once decreases, and then increases again due to T _inertia . It shows the complicated behavior.

When misfire occurs in the internal combustion engine 10, the cylinder gas pressure torque T _gas cannot be increased due to the explosion of the air-fuel mixture in the misfired cylinder. As a result, the indicated torque _Ti is temporarily reduced, so that the angular acceleration dω / dt of the crankshaft 24 is also temporarily reduced. For this reason, misfire can be detected from the angular acceleration dω / dt of the crankshaft 24. However, as shown above, the indicated torque T _i exhibits a complicated behavior not only due to the influence of the cylinder gas pressure torque T _gas but also due to the influence of the inertia torque T _inertia due to the reciprocating inertia mass. Therefore, if the influence of the inertia torque T _inertia cannot be excluded, it is difficult to accurately detect in which cylinder the misfire has occurred. Therefore, in this embodiment, the influence of the inertia torque T _inertia due to the reciprocating inertia mass is eliminated as follows.

When attention is paid to a section with a crank angle of 180 ° from TDC to BDC, the average value of the inertia torque T _inertia due to the reciprocating inertia mass in this section is zero. This is because the member having the reciprocating inertia mass moves in the opposite direction at a crank angle of about 0 ° to 90 ° and a crank angle of about 90 ° to 180 °. Therefore, when the torques of the equations (1) and (2) are calculated as average values from TDC to BDC, the inertia torque T _inertia = 0 due to the reciprocating inertia mass can be calculated. Thereby, it is possible to eliminate the influence of the inertia torque T _inertia due to the reciprocating inertia mass on the indicated torque T _i .

That is, when the average value of each torque is obtained in the section from TDC to BDC, the average value of the inertia torque T _inertia becomes zero. Therefore, if the average value of the angular acceleration dω / dt of the crankshaft 24 is obtained in the same section, the angular acceleration dω / dt can be obtained without the influence of the reciprocating inertial mass.

Hereinafter, a specific calculation method of the angular acceleration dω / dt in the present embodiment will be described. FIG. 3 is a schematic diagram illustrating a method for calculating the angular acceleration of the crankshaft 24. As shown in FIG. 3, in this embodiment, a crank angle signal is detected from the crank angle sensor 42 every 10 ° of rotation of the crankshaft 24. Then, angular velocities ω ₀ (k) and ω ₀ (k + 1) are obtained at two crank angle positions of TDC and BDC, respectively, and a time Δt (k) during which the crankshaft 24 rotates from TDC to BDC is obtained.

When obtaining the angular velocity ω ₀ (k), for example, as shown in FIG. 3, the time Δt ₀ (k) and Δt ₁₀ (k) during which the crank angle is rotated 10 ° forward and backward from the TDC position are calculated. It is detected from the crank angle sensor 42. Since the crankshaft 24 rotates 20 ° during the time Δt ₀ (k) + Δt ₁₀ (k), ω ₀ (k) = (20 / (Δt ₀ (k) + Δt ₁₀ (k))) By calculating x (π / 180 °), ω ₀ (k) [rad / s] can be calculated. Similarly, when calculating ω ₀ (k + 1), times Δt ₀ (k + 1) and Δt ₁₀ (k + 1) are detected while the crank angle is rotating 10 ° forward and backward from the BDC position. _{Then, ω 0 (k + 1)} = (20 / (Δt 0 (k + 1) + Δt 10 (k + 1))) × (π / 180 °) ω by computing ₀ (k + 1) can be calculated [rad / s].

After obtaining the angular velocities ω ₀ (k), ω ₀ (k + 1) as described above, by calculating (ω ₀ (k + 1) −ω ₀ (k)) / Δt (k), TDC to BDC The average value of the angular acceleration dω / dt during the rotation of the crankshaft 24 can be calculated.

  FIG. 4 is a diagram for explaining a misfire detection method according to the present embodiment. In FIG. 4, the horizontal axis represents the crank angle. The upper part of FIG. 4 shows the stroke of each cylinder of the internal combustion engine 10. As shown in this figure, the explosion order of an in-line four-cylinder engine such as the internal combustion engine 10 of the present embodiment is normally # 1 → # 3 → # 4 → # 2 (# is a cylinder number). Note that TDC and BDC shown in FIG. 4 are those of the # 1 cylinder and # 4 cylinder, and the opposite is true for the # 2 cylinder and # 3 cylinder.

  As shown in the lower part of FIG. 4, the ECU 50 sequentially calculates the angular acceleration dω / dt of the crankshaft 24 according to the above-described method for each expansion stroke of each cylinder. When the calculated angular acceleration dω / dt falls below a predetermined misfire determination threshold, it is determined that misfire has occurred in the cylinder. In the example shown in FIG. 4, the angular acceleration dω / dt calculated during the expansion stroke of the # 1 cylinder is below the misfire determination threshold. Therefore, in this case, it can be determined that a misfire has occurred in the # 1 cylinder.

  In the misfired cylinder, the air-fuel mixture in the cylinder is discharged from the exhaust valve 36 without being burned. For this reason, exhaust gas containing a large amount of unburned HC (hereinafter referred to as “unburned gas”) is discharged from the exhaust valve 36 from the misfired cylinder in the subsequent exhaust stroke. When the exhaust purification catalyst 26 has been warmed up and activated, such unburned HC is purified by the exhaust purification catalyst 26. However, uncombusted HC cannot be purified by the exhaust purification catalyst 26 when the exhaust purification catalyst 26 is not activated, just after the cold start of the internal combustion engine 10.

  By the way, when the internal combustion engine 10 is at a low temperature, such as immediately after a cold start, if external EGR is executed, the in-cylinder combustion becomes unstable due to the influence of the inert gas, which tends to cause idle operation failure. For this reason, immediately after the cold start, as a rule, the EGR valve 48 is closed and the external EGR is stopped. Accordingly, when misfire occurs in this case, all the unburned gas discharged from the misfire cylinder flows to the exhaust purification catalyst 26. Therefore, there is a problem that a large amount of HC contained in the unburned gas passes through the exhaust purification catalyst 26 in the inactive state and is released into the atmosphere as it is.

  In order to solve such a problem, in the present embodiment, the following control is performed. That is, in this embodiment, when the unburned gas is discharged from the exhaust valve 36 of the misfire cylinder, the EGR valve 48 is temporarily set so that the unburned gas flows back to the intake passage 16 through the EGR passage 46. Open. Thereby, since unburned gas can be recirculated to a combustion chamber and burned, discharge | release of unburned HC to air | atmosphere can be suppressed reliably. In this case, the main component that recirculates to the intake passage 16 is not an inert gas but an unburned gas (that is, a mixture of fuel and air). For this reason, even if the EGR valve 48 is temporarily opened, the air-fuel ratio A / F in the combustion chamber does not change and the combustion does not become unstable. Therefore, no idle operation failure occurs.

  FIG. 5 is a diagram illustrating a control method of the EGR valve 48 when the unburned gas discharged from the misfire cylinder is recirculated to the intake passage 16 through the EGR passage 46. In order to allow the unburned gas discharged from the exhaust valve 36 of the misfire cylinder to flow into the EGR passage 46, the EGR valve 48 is opened at the timing when the unburned gas reaches the branch portion between the exhaust passage 18 and the EGR passage 46. The EGR valve 48 may be closed when all the unburned gas is introduced into the EGR passage 46. The time required for the exhaust gas to flow from the exhaust valve 36 to the branch portion to the EGR passage 46 (hereinafter referred to as “transport delay time”) is the distance from the exhaust valve 36 to the branch portion as the exhaust gas flow rate. It can be calculated by dividing. The exhaust gas flow rate is proportional to the exhaust gas flow rate. The exhaust gas flow rate correlates with the intake air amount. Therefore, in this embodiment, the transport delay time can be calculated based on the intake air amount detected by the air flow meter 23. As shown in FIG. 5, in the present embodiment, when misfire is detected, the transportation is performed from the timing after the transportation delay time from the exhaust valve opening timing of the misfiring cylinder from the exhaust valve closing timing of the misfire cylinder. The EGR valve 48 is opened until a time point later than the delay time. Thereby, the unburned gas discharged from the misfired cylinder can be accurately taken into the EGR passage 46.

[Specific Processing in Embodiment 1]
FIG. 6 is a flowchart of a routine executed by the ECU 50 in the present embodiment in order to realize the above function. This routine is executed after a cold start of the internal combustion engine 10 (when the exhaust purification catalyst 26 is inactive). As described above, after the cold start, as a rule, the EGR valve 48 is closed and the external EGR is stopped in order to prevent idle operation failure.

  After the cold start, the angular acceleration dω / dt of the crankshaft 24 is sequentially calculated for each expansion stroke of each cylinder according to the above-described method (step 100). Then, the presence or absence of misfire is determined by comparing the calculated angular acceleration dω / dt with a predetermined misfire determination threshold (step 102).

  If the angular acceleration dω / dt falls below the misfire determination threshold in step 102, it is determined that misfire has occurred in the cylinder. In this case, next, a transport delay time Td is calculated (step 104). In step 104, the exhaust gas flow rate is calculated based on the intake air amount detected by the air flow meter 23, and the transport delay time Td is calculated based on the exhaust gas flow rate.

  Subsequently, it is determined whether or not the timing after the exhaust valve opening timing of the cylinder where the misfire has been detected has arrived after the transportation delay time Td calculated in step 104 (step 106). When this timing arrives, it can be determined that the unburned gas discharged from the exhaust valve 36 of the misfired cylinder has reached the branch portion between the exhaust passage 18 and the EGR passage 46. Therefore, after waiting for this timing, the EGR valve 48 is opened (step 108).

  Subsequently, it is determined whether or not the timing after the exhaust valve closing timing of the cylinder where the misfire has been detected has arrived after the transportation delay time Td calculated in step 104 (step 110). When this timing arrives, it can be determined that all unburned gas discharged from the exhaust valve 36 of the misfired cylinder has been introduced into the EGR passage 46. Therefore, after waiting for this timing, the EGR valve 48 is closed (step 112).

  As described above, according to the present embodiment, when a misfire occurs when the exhaust purification catalyst 26 is inactive, the unburned gas discharged from the misfire cylinder is recirculated to the combustion chamber to be used for combustion. Can do. For this reason, it can suppress reliably that unburned HC is discharge | released in air | atmosphere. In this case, it is mainly the unburned gas, not the inert gas, that returns to the intake passage 16. Therefore, since the ratio of the inert gas in the combustion chamber does not increase, even if the temperature of the internal combustion engine 10 is low as it is immediately after the cold start, no malfunction is caused.

  Further, in the present embodiment, the average crank angular acceleration in the crank angle section where the average value of the inertia torque due to the reciprocating inertia mass of the internal combustion engine 10 is approximately zero is calculated, and the occurrence of misfire and its A misfired cylinder is detected. Thereby, it is possible to accurately determine the occurrence of misfire and the misfire cylinder. Further, it is not necessary to provide a special sensor (cylinder pressure sensor or the like), and the cost can be reduced.

  In the above example, the present invention is applied to a four-cylinder internal combustion engine. However, even in an internal combustion engine other than the four-cylinder engine, a section where the average value of inertia torque due to reciprocating inertia mass is 0 (720 ° CA / The present invention can be similarly applied by calculating the average crank angular velocity in the number of cylinders).

  In the present embodiment, the case where one cylinder misfires has been described as an example. However, the present invention can be similarly applied to a case where a plurality of cylinders continuously misfire.

  In the first embodiment described above, the ECU 50 executes the processes of steps 100 and 102, so that the “misfire detection means” in the first invention executes the processes of steps 104 to 112. The “unburned gas recirculation means” in the first invention realizes the “transport delay time calculation means” in the second invention by executing the processing of step 104 described above.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIG. 7. The description will focus on the differences from the above-described embodiment, and the description of the same matters will be simplified or omitted. To do. The hardware configuration of this embodiment is the same as that of the first embodiment described above.

  In the present embodiment, a learning value for correcting the transport delay time Td is calculated based on the detection result of the air-fuel ratio sensor 54. As described above, the transport delay time Td is determined by the distance from the exhaust valve 36 to the branch portion to the EGR passage 46 and the exhaust gas flow velocity. The exhaust gas flow rate is proportional to the exhaust gas flow rate. However, the proportional relationship may change as the internal combustion engine 10 changes over time. For example, if deposits are accumulated on the inner wall of the exhaust passage 18, the flow passage cross-sectional area of the exhaust passage 18 is reduced, so that the flow rate is increased even when the exhaust gas flow rate is the same. For this reason, an error occurs in the calculated transport delay time Td.

  If an error occurs in the calculated transport delay time Td, there is a difference between the timing when the unburned gas from the misfired cylinder reaches the branch portion to the EGR passage 46 and the timing when the EGR valve 48 is opened and closed. As a result, a part of the unburned gas may flow downstream of the exhaust passage 18 or the inert gas (burned gas) may return to the combustion chamber via the EGR passage 46 to deteriorate combustion. .

  In this embodiment, the error of the transport delay time Td due to the secular change as described above is corrected as follows. FIG. 7 is a diagram showing the output of the air-fuel ratio sensor 54 when a misfire occurs. The air-fuel ratio of the internal combustion engine 10 is controlled to fall within a desired air-fuel ratio width by known air-fuel ratio feedback control. When the unburned gas generated from the misfired cylinder is correctly recirculated to the intake passage 16 through the EGR passage 46, the air-fuel ratio in the combustion chamber does not change, so the exhaust air-fuel ratio detected by the air-fuel ratio sensor 54 is There is no deviation.

  However, if an error occurs in the transport delay time Td, the opening period of the EGR valve 48 deviates from an appropriate period by the error. In the shifted period, the inert gas recirculates to the combustion chamber instead of the unburned gas. When the inert gas returns to the combustion chamber, the air-fuel ratio shifts to the lean side, so that the exhaust air-fuel ratio detected by the air-fuel ratio sensor 54 deviates from the desired air-fuel ratio width as shown in FIG. This period, that is, the period during which the exhaust air-fuel ratio deviates from the desired air-fuel ratio width (hereinafter referred to as “air-fuel ratio disturbance period”) td corresponds to the period during which the inert gas is recirculated to the combustion chamber. This corresponds to an error occurring in the transport delay time Td.

  Accordingly, if the transport delay time Td is corrected by the air-fuel ratio disorder period td, an appropriate transport delay time Td can be calculated. However, the air-fuel ratio disturbance period td is inversely proportional to the exhaust gas flow rate. Therefore, in the present embodiment, the air-fuel ratio disturbance period td is calculated based on the output of the air-fuel ratio sensor 54, and “air-fuel ratio disturbance period td / exhaust gas flow rate” that is a transport delay time correction value per unit flow rate is learned. It was decided to calculate as a value. In step 104 of FIG. 6 described above, the transport delay time Td is corrected by adding a correction value obtained by multiplying the learned value by the exhaust gas flow rate to the transport delay time Td.

  According to this embodiment, as described above, the transport delay time Td can be appropriately corrected based on the learned value. For this reason, even when the aging of the internal combustion engine 10 occurs, the unburned gas discharged from the misfire cylinder can be recirculated to the combustion chamber with high accuracy, and the unburned HC is released into the atmosphere. It can suppress more reliably. In the present embodiment, an oxygen sensor may be used instead of the air-fuel ratio sensor 54.

  In the second embodiment described above, the air-fuel ratio sensor 54 corresponds to the “air-fuel ratio detecting means” in the third aspect of the present invention. Further, the ECU 50 obtains “the air-fuel ratio disturbance period td / exhaust gas flow rate” as a learned value, and thus the “learning means” in the third aspect of the invention obtains a correction value obtained by multiplying the learned value by the exhaust gas flow rate. Is added to the transport delay time Td, the “transport delay time correcting means” in the third aspect of the present invention is realized.

Embodiment 3 FIG.
Next, the third embodiment of the present invention will be described with reference to FIG. 8. The description will focus on the differences from the above-described embodiment, and the description of the same matters will be simplified or omitted. To do. The hardware configuration of this embodiment is the same as that of Embodiment 1 described above, except that the internal combustion engine 10 is a V-type 8-cylinder.

  In the four-cylinder engine as in the first embodiment described above, the strokes of the cylinders are shifted by 180 ° CA, so that the exhaust valve opening periods of the cylinders do not overlap in time. On the other hand, in an engine having a larger number of cylinders, the time overlap between the exhaust valve opening periods of the cylinders becomes larger.

  FIG. 8 is a diagram showing the overlap of the exhaust valve opening periods of the respective cylinders of the V-type 8-cylinder engine. As shown in FIG. 8, when a misfire occurs in a certain cylinder, the first half of the exhaust valve opening period of this cylinder overlaps with the exhaust valve opening period of the cylinder in which the explosion order is one previous, In the second half of the exhaust valve opening period of the cylinder, the explosion valve overlaps with the exhaust valve opening period of the next cylinder. For this reason, when trying to take in the unburned gas from the misfired cylinder into the EGR passage 46, a part of the exhaust gas from the previous and next cylinder in the explosion order is also introduced into the EGR passage 46 together with the unburned gas. Will be captured. As a result, the inert gas recirculates into the combustion chamber, which may deteriorate the air-fuel ratio controllability.

  In the present embodiment, the following control is performed to prevent the deterioration of the air-fuel ratio controllability as described above. In this embodiment, when the EGR valve 48 is temporarily opened to recirculate the unburned gas in the misfired cylinder, the ratio of the inert gas in the gas recirculated through the EGR passage 46 is based on the following equation. To calculate.

Inert gas ratio = (gas amount in the overlap section) /
(Gas amount of misfire cylinder + Gas amount of overlap section)

  In the above equation, “the gas amount in the overlap section” means that, as described with reference to FIG. 8, the misfire cylinder and the other cylinder in which the exhaust valve opening period overlap are exhausted in the overlap section. Means the amount of exhaust gas (ie, inert gas). The amount of gas in the misfiring cylinder and the amount of gas in the overlap section can be calculated for each cylinder based on the exhaust gas flow velocity and the exhaust valve opening period, respectively.

  In the present embodiment, the fuel injection amount from the fuel injector 28 is corrected based on the inert gas ratio calculated as described above. That is, the fuel injection amount is increased as the inert gas ratio increases. Thereby, it is possible to reliably prevent the air-fuel ratio from shifting to the lean side due to the influence of the inert gas, and to improve the air-fuel ratio controllability.

  In this embodiment, the case of a V-type 8-cylinder engine has been described as an example. However, the present invention can be similarly applied to a V-type 6-cylinder engine, a V-type 12-cylinder engine, and the like.

  In the third embodiment described above, the “inert gas ratio calculating unit” and the “fuel injection amount correcting unit” are realized by the ECU 50 performing the above-described control.

Embodiment 4 FIG.
Next, the fourth embodiment of the present invention will be described with reference to FIG. 9 and FIG. 10. The difference from the above-described first embodiment will be mainly described, and the same matters will be described. Simplify or omit.

  FIG. 9 is a diagram for explaining a system configuration according to the fourth embodiment of the present invention. In FIG. 9, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted or simplified. As shown in FIG. 9, a bypass passage 60 that bypasses the exhaust passage 18 is provided in the middle of the exhaust passage 18 of the internal combustion engine 10 of the present embodiment. In the middle of the bypass passage 60, an HC adsorbent 62 having a function of adsorbing unburned HC in the exhaust gas is installed. As the HC adsorbent 62, for example, activated carbon or zeolite can be used.

  At the branching portion where the bypass passage 60 branches from the exhaust passage 18, it is possible to switch between a state where the exhaust gas flows into the bypass passage 60 and a state where the exhaust gas flows directly downstream of the exhaust passage 18 without flowing through the bypass passage 60. A flow path switching valve 64 is installed. The flow path switching valve 64 is controlled by the ECU 50.

  In the present embodiment, when the exhaust purification catalyst 26 is inactive, such as immediately after a cold start, if misfire occurs and unburned gas flows into the exhaust passage 18, the flow is switched from the exhaust valve 36. By controlling the flow path switching valve 64 based on the transport delay time to the valve 64, the unburned gas is allowed to flow into the bypass passage 60. Thereby, HC in unburned gas can be adsorbed by the HC adsorbent 62, and release of unburned HC into the atmosphere can be suppressed.

  Further, according to the present embodiment, exhaust gas can be prevented from flowing into the bypass passage 60 except when unburned gas from the misfired cylinder is taken into the bypass passage 60. This has the following advantages.

  As a first advantage, it is possible to prevent the HC adsorbent 62 from becoming full of HC. That is, since the adsorption capacity of the HC adsorbent 62 is limited, if the exhaust gas continues to flow through the HC adsorbent 62, the HC adsorbent 62 becomes full of HC. Then, when misfire occurs and unburned gas containing a large amount of HC is discharged, HC cannot be adsorbed and HC is released into the atmosphere. According to the present embodiment, such a situation can be reliably avoided, and unburned HC from the misfired cylinder can be reliably adsorbed to the HC adsorbent 62.

  As a second advantage, the temperature rise of the HC adsorbent 62 can be reliably suppressed. The HC adsorbent 62 has the property of releasing adsorbed HC when the temperature rises. For this reason, if the exhaust gas continues to flow through the HC adsorbent 62, the temperature of the HC adsorbent 62 rises, the adsorbed HC is released, and the HC is released into the atmosphere. Further, when the temperature of the HC adsorbent 62 rises, the deterioration of the HC adsorbent 62 proceeds. According to this embodiment, these situations can be avoided reliably.

  A method for purifying HC adsorbed on the HC adsorbent 62 is not particularly limited, but in the present embodiment, for example, the following method can be used. After the exhaust purification catalyst 26 is activated, the flow path switching valve 64 is opened little by little to allow a part of the exhaust gas to flow through the HC adsorbent 62. As a result, the temperature of the HC adsorbent 62 is raised to the HC desorption temperature to desorb HC. The separated HC is purified by the exhaust purification catalyst 26.

[Specific Processing in Embodiment 4]
FIG. 10 is a flowchart of a routine executed by the ECU 50 in the present embodiment in order to realize the above function. This routine is executed after a cold start of the internal combustion engine 10 (when the exhaust purification catalyst 26 is inactive).

  After the cold start, the angular acceleration dω / dt of the crankshaft 24 of the internal combustion engine 10 is calculated to detect misfire (step 120). The processing in step 120 is the same as that in step 100 in FIG. Next, the presence / absence of misfire is determined by comparing the angular acceleration dω / dt calculated in step 120 with a predetermined misfire determination threshold value (step 122).

  If the angular acceleration dω / dt falls below the misfire determination threshold in step 122, it is determined that misfire has occurred in the cylinder. In this case, the transport delay time Td is then calculated (step 124). In this step 124, the exhaust gas flow rate is calculated based on the intake air amount detected by the air flow meter 23, and the transport delay time Td from the exhaust valve 36 to the flow path switching valve 64 is calculated based on the exhaust gas flow rate. Is done.

  Subsequently, it is determined whether or not the timing after the transport delay time Td calculated in step 124 has arrived from the exhaust valve opening timing of the cylinder where the misfire has been detected (step 126). When this timing arrives, it can be determined that the unburned gas discharged from the exhaust valve 36 of the misfired cylinder has reached the flow path switching valve 64. Therefore, after the arrival of this timing, the flow path switching valve 64 is opened so that the exhaust gas flows into the bypass passage 60 (step 128).

  Subsequently, it is determined whether or not the timing after the exhaust valve closing timing of the cylinder where the misfire has been detected has arrived after the transportation delay time Td calculated in step 124 (step 130). When this timing arrives, it can be determined that all the unburned gas discharged from the exhaust valve 36 of the misfired cylinder has been introduced into the bypass passage 60. Therefore, after the arrival of this timing, the flow path switching valve 64 is closed so that the exhaust gas does not flow into the bypass passage 60 (step 132).

  According to the routine process shown in FIG. 10 described above, the exhaust gas can be allowed to flow through the bypass passage 60 only when unburned gas from the misfired cylinder comes. For this reason, HC in unburned gas can be reliably adsorbed by the HC adsorbent 62. Further, it is possible to reliably prevent the HC adsorbing material 62 from being filled with HC or the temperature of the HC adsorbing material 62 from rising and the adsorbed HC from separating.

  In the above-described fourth embodiment, the ECU 50 executes the processes of steps 120 and 122, so that the “misfire detection means” in the fifth aspect of the invention executes the processes of steps 124 to 132. The “adsorption control means” in the fifth invention is realized.

It is a figure for demonstrating the system configuration | structure of Embodiment 1 of this invention. It is a figure which shows the characteristic of illustration torque, in-cylinder gas pressure torque, and inertia torque. It is a schematic diagram which shows the method of calculating the angular acceleration of a crankshaft. It is a figure for demonstrating the misfire detection method in Embodiment 1 of this invention. It is a figure which shows the EGR valve control method in the case of returning the unburned gas discharged | emitted from the misfire cylinder to an intake passage through an EGR passage. It is a flowchart of the routine performed in Embodiment 1 of the present invention. It is a figure which shows the output of the air fuel ratio sensor in case a misfire occurs. It is a figure which shows the overlap of the exhaust valve opening period of each cylinder of a V type 8 cylinder engine. It is a figure for demonstrating the system configuration | structure of Embodiment 4 of this invention. It is a flowchart of the routine performed in Embodiment 4 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Piston 16 Intake passage 18 Exhaust passage 20 Throttle valve 22 Surge tank 23 Air flow meter 24 Crankshaft 26 Exhaust purification catalyst 28 Fuel injector 32 Intake valve 36 Exhaust valve 42 Crank angle sensor 44 Accelerator position sensor 46 EGR passage 48 EGR valve 50 ECU
52 Water temperature sensor 54 Air-fuel ratio sensor 60 Bypass passage 62 HC adsorbent 64 Channel switching valve

Claims (6)

An EGR passage connecting an exhaust passage and an intake passage of the internal combustion engine;
An EGR valve that opens and closes the EGR passage;
A crank angle sensor for detecting a rotation angle of a crankshaft of the internal combustion engine;
Misfire detection means for detecting the occurrence of misfire based on the signal of the crank angle sensor;
When the EGR is stopped by closing the EGR valve, if misfire is detected by the misfire detection means, unburned gas discharged from the misfired cylinder passes through the EGR passage and the intake passage. Unburned gas recirculation means for temporarily opening the EGR valve so as to recirculate to
A control device for an internal combustion engine, comprising: A transport delay time calculating means for calculating a transport delay time of the exhaust gas from the exhaust valve to the EGR passage;
2. The control of an internal combustion engine according to claim 1, wherein the unburned gas recirculation means opens the EGR valve during a period in which an exhaust valve opening period of the misfired cylinder is delayed by the calculated transport delay time. apparatus. Air-fuel ratio detecting means for detecting the air-fuel ratio;
Learning means for acquiring a learning value for correcting the transport delay time based on a detection result of the air-fuel ratio detection means;
Transport delay time correcting means for correcting the transport delay time based on the learned value;
The control apparatus for an internal combustion engine according to claim 2, further comprising: In the internal combustion engine, exhaust valve opening periods of a plurality of cylinders overlap in time,
When the EGR valve is temporarily opened by the unburned gas recirculation means, the exhaust valve opening overlapping the exhaust valve opening period of the misfired cylinder is added to the gas recirculating to the intake passage through the EGR passage. An inert gas ratio calculating means for calculating a ratio of the inert gas discharged from the cylinder having the valve period;
Fuel injection amount correcting means for correcting the fuel injection amount based on the ratio calculated by the inert gas ratio calculating means;
The control apparatus for an internal combustion engine according to any one of claims 1 to 3, further comprising: A bypass passage for bypassing the exhaust passage of the internal combustion engine;
An HC adsorbent provided in the bypass passage and having a function of adsorbing HC in the exhaust gas;
A flow path switching valve that switches between a state of flowing exhaust gas through the bypass passage and a state of not flowing the exhaust gas;
A crank angle sensor for detecting a rotation angle of a crankshaft of the internal combustion engine;
Misfire detection means for detecting the occurrence of misfire based on the signal of the crank angle sensor;
When the misfire is detected by the misfire detection means without always flowing the exhaust gas through the bypass passage, the unburned gas discharged from the misfired cylinder is caused to flow temporarily through the bypass passage. Adsorbing control means for controlling the flow path switching valve so as to pass through the HC adsorbent,
A control device for an internal combustion engine, comprising:   The misfire detection means detects the occurrence of misfire based on an average crank angular acceleration in a crank angle section where an average value of inertia torque due to reciprocating inertial mass of the internal combustion engine is substantially zero. Item 6. The control device for an internal combustion engine according to any one of Items 1 to 5.

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